Diagnostic performance obtainable from radiographic systems is limited necessarily by sampling constraints which preclude uniform access to dynamic processes manifested in the three spatial dimensions as well as time. Conventionally, improvements in diagnostic performance have been effected by manipulation of the temporal limitations through immobilization of the object of diagnostic interest.
When temporal limitations are ignored, diagnostic performance can be enhanced through an increase in the range and number of x-ray projections produced. Early conventional bases for optimizing diagnostic performance simply involved taking multiple transmission radiographs from projection angles judged to be appropriate for the diagnostic task. When anatomical constraints precluded access to unambiguous single-projection geometries, supplemental approaches were developed involving the use of linear, circular, and hypercycloidal tomography.
A more recent improvement over conventional tomography is tomosynthesis. The primary advantage afforded by tomosynthesis over conventional tomography resides in the fact that tomosynthesis enables any number of tomographic slices to be reconstructed from a single scanning sequence of x-ray exposures. However, one of the drawbacks with the practical implementation of conventional tomosynthetic systems has been that acquisition of all tomosynthetic projections must be made with little or no movement of the irradiated tissues or objects. Only by immobilizing the object of interest is it presently possible to establish the known geometric relationships required for conventional tomosynthetic reconstruction systems.
The advent of modern computerized tomography has greatly improved diagnostic performance of conventional tomography and tomosynthesis by facilitating access to tissue or object details visible only through 2- or 3-dimensional sampling in a way that eliminates tomographic blur. However, even computerized tomography has significant shortcomings, particularly for tasks requiring high spatial resolution or the need to track tissue or object changes over extended periods of time.
Unfortunately, computerized tomography is expensive and cumbersome. Another drawback with conventional computerized tomography is that it is limited predominantly to examination of axial tissues. Computerized tomography is not easily adapted for use on extremities or breast tissues. Furthermore, computerized tomography is confined to applications which are not limited by the intrinsically low spatial resolution of computerized tomography.
Computerized tomography is also intimidating to many patients and requires nearly complete patient immobilization for relatively extended periods of time. Requiring patient immobilization over extended periods of time restricts the degree to which long-term temporal changes can be tracked. It is virtually impossible to reposition a patient in exactly the same way from one examination to another. As a result, changes in patient position tend to be confounded with tissue changes of diagnostic interest.
Similar problems are encountered with the application of conventional tomosynthesis and computerized tomography in industrial applications. The use of conventional tomosynthesis and computerized tomography is constrained. Both technologies require that the object of radiographic interest bear a fixed geometric relationship to all of the multiple projection geometries required to implement image reconstruction. Any change in projection geometry mediated by unanticipated object motion relative to the x-ray source, either during or between exposures, precludes accurate reconstruction.
A system, method, and device for self-calibrating tomosynthesis are provided by the present invention which overcome many of the constraints of conventional tomosynthesis or computerized tomography. Significantly, the need for immobilization of the irradiated object during the sequence of multiple exposures required for tomosynthetic reconstruction is eliminated. In accordance with the present invention, a calibrated radiographic imager device is affixed to the object of interest, thereby enabling the required projection geometry underlying individual projections to be determined after exposure from random or arbitrary positions of the x-ray source relative to the object of interest and the radiographic imager.